JP4827180B2 - Work vehicle - Google Patents

Description

  The present invention relates to a work vehicle such as a snowplow.

  In a snowplow having a traveling system HST and a work implement system HST operatively driven by an engine, when the load on the work implement system HST exceeds a predetermined value, the output of the travel system HST is automatically generated according to the load. Thus, a configuration has been proposed in which the work system HST is automatically prevented from being overloaded (see the following patent document).

  The conventional configuration is useful in that an operator can manually prevent the output of the traveling system HST without overloading the work system HST, but there is room for improvement in terms of work efficiency.

More specifically, in the conventional configuration, the load of the work implement system HST is detected based on the hydraulic pressure in the work implement system HST, and the movable swash plate of the travel system HST is tilted in the deceleration direction according to the load. It has become so.
In such a conventional configuration, even when the engine has a margin, if the working hydraulic pressure of the work implement system HST exceeds a predetermined threshold, the movable swash plate of the traveling system HST is uniformly inclined in the deceleration direction. As a result, the traveling speed of the vehicle is reduced below the target speed corresponding to the operation position of the speed change operation member, and as a result, work takes time.

In the conventional configuration, the traveling system HST is a swash plate control type that controls the tilt position of the movable swash plate in accordance with the operation position of the speed change operation member.
In such a configuration, for example, when a load is applied to the traveling unit, such as when traveling on an uphill, the actual vehicle speed is changed regardless of the load on the working unit. The speed is lower than the target vehicle speed according to the operation position of the member.
In other words, in the conventional configuration, even when the load on the working unit is equal to or less than a predetermined threshold, when the load is applied to the traveling unit, the vehicle speed is uniformly set regardless of whether the engine has a margin. Is lower than the target vehicle speed. Accordingly, work efficiency is deteriorated.

JP-A-7-173810

  The present invention has been made in view of the above-described prior art, and is a working vehicle including a traveling unit and a working unit that are driven using output from an engine, and prevents overloading the engine. Another object is to provide a working vehicle that can prevent a reduction in working efficiency as much as possible.

In order to achieve the above-mentioned object, the present invention achieves the HST (Hydro Static) inserted in the traveling part and working part driven using the output from the engine and the traveling system transmission path from the engine to the traveling part. Transmission; hydrostatic continuously variable transmission), a shift operation member for shifting the HST, an engine output detection device for detecting the output rotation speed of the engine, and a running output detection for detecting the rotation output of the HST Device, an operation amount detection device for detecting an operation amount of the speed change operation member, an input signal for detection from the engine output detection device, the travel output detection device, and the operation amount detection device, and an output adjustment member in the HST A control unit that outputs a control signal of the engine output based on a detection result of the engine output detection device with respect to a reference output corresponding to an operation amount of the speed change operation member. A load control mode for controlling the operation of the output adjusting member using an output multiplied by a deceleration rate as a target rotation output of the HST, and the load control mode is based on a signal from the engine output detection device; When the engine output speed exceeds the first threshold, the deceleration rate is set to 1, and when the engine output speed is equal to or less than the first threshold, the deceleration rate corresponding to the output speed is selected , When the engine output rotational speed becomes equal to or smaller than a second threshold value smaller than the first threshold value, the operation of the output adjusting member is controlled so that the rotational output of the HST becomes zero, and the engine output rotational speed is set to the first threshold value. If the target rotational output after multiplication of the deceleration rate falls below a predetermined minimum output when it is less than or equal to the threshold and greater than the second threshold, the rotational output of the HST becomes the minimum output. Providing a working vehicle for performing operation control of the output adjusting member so.
For example, the control unit may be configured to select a deceleration rate that decreases as the output rotational speed decreases when the output rotational speed of the engine becomes equal to or less than the first threshold value.

  In the work vehicle according to the present invention, the control unit includes a vehicle speed control mode in which operation control of the output adjustment member is performed with a reference output corresponding to an operation amount of the speed change operation member as a target rotation output of the HST. The vehicle speed control mode or the load control mode may be switched by a manually operable changeover switch.

In the working vehicle according to the present invention, the HST typically includes a pump shaft (input shaft) operatively connected to the drive source, and a pump main body supported on the pump shaft so as not to be relatively rotatable. A motor body fluidly connected to the pump body via a pair of hydraulic oil lines, a motor shaft (output shaft) rotated about an axis by the motor body, and at least the pump body or the motor body The thing provided with the output adjustment member which changes one supply-and-discharge oil amount can be illustrated.
The HST may be configured such that the output shaft rotates only in one direction with one end of the output range as a neutral position, or an arbitrary position (for example, an intermediate position) between one end and the other end of the output range. The output shaft may be configured to rotate in one direction or the other direction with the neutral position as a boundary.

  Further, in the work vehicle according to the present invention, a work clutch device inserted in a work system transmission path from the engine to the work part, and a work clutch operation for performing a predetermined manual operation on the work clutch device. And a member.

In the working vehicle according to the present invention, a control section is an output obtained by multiplying the deceleration rate based on the detection result of the engine output sensing device relative to the reference output corresponding to the operation amount of the shift operating member as the target rotational output of the HST A load control mode for controlling the operation of the output adjusting member of the HST, and the load control mode is configured such that when the output speed of the engine exceeds the first threshold, the operation amount of the speed change operation member since the operation control of the output adjusting member an output obtained by multiplying 1 as pre-Symbol deceleration rate as a target rotational output of the HST with respect to a reference output in accordance with, before load is applied to the running portion of the working vehicle If the load on the serial engine is smaller than a predetermined value, the output of the HST is maintained at the reference output, can prevent a decrease in vehicle speed, it is possible to prevent as much as possible the reduction of the thus work efficiency
In the load control mode, when the output speed of the engine is equal to or less than the first threshold value, a reference output corresponding to the operation amount of the speed change operation member is multiplied by the deceleration rate corresponding to the output speed. since the operation control of the output adjusting member output as the target rotational output of the HST, it is possible to prevent overloading to the engine.
Further, in the load control mode, the rotation output of the HST becomes zero when the output speed of the engine falls below a second threshold value that is smaller than the first threshold value based on a signal from the engine output detection device. Since the operation of the output adjusting member is controlled, it is possible to reliably prevent the occurrence of inconvenience such as engine stall even when a load is applied to the engine such that the output speed of the engine is less than the second threshold value. It becomes.
Further, in the load control mode, when the output speed of the engine is equal to or less than the first threshold value and greater than the second threshold value, the target rotation output after multiplication of the deceleration rate falls below a predetermined minimum output Because the operation of the output adjusting member is controlled so that the rotation output of the HST becomes the minimum output, the HST target rotation output after multiplication of the deceleration rate is necessary even though the engine has a margin. It can prevent that it falls more than it, and can improve work efficiency that much.

Further, the control section, the speed-change operating Bei give a vehicle speed control mode for controlling operation of the output adjusting member as a target rotational output of the reference output the HST in accordance with the operation amount of the member, the manual operation can be changeover switch When the vehicle speed control mode or the load control mode is configured to be switched, for example, the vehicle speed control mode can be switched to the load control mode by the changeover switch during work, and the vehicle speed control can be performed by the changeover switch during non-working. You can switch to mode.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic side view of a walking snowplow 1 as an example of a working vehicle according to the present invention, and FIG. 2 is a schematic plan view of the walking snowplow 1 shown in FIG.

  The working vehicle 1 shown in FIG. 1 and FIG. 2 includes a traveling unit 40L, 40R and a working unit 20 that are driven using the output from the engine 31, and a traveling system transmission from the engine 31 to the traveling unit 40L, 40R. HST102 inserted in the path | route and the speed change operation member 53 for speed-change-operating the said HST102 are provided.

Specifically, the working unit 20 is a snow removal unit here, and is configured to remove snow on the traveling road of the working vehicle 1.
Specifically, the working unit 20 is supported by the machine frame 10 in the front-and-rear direction x1 of the machine frame 10 (see arrow x in FIG. 1), and a scraping auger 21 that scrapes snow. An auger housing 22 that covers the scraping auger 21, a blower housing 23 that is disposed in the longitudinal direction x rear x 2 of the auger housing 22, a blower 24 that is built in the blower housing 23, And a shooter 25 disposed above.

The scraping auger 21 scrapes snow on the traveling path of the work vehicle 1 toward the center of the body (see the arrow y in FIG. 2) and sends it to the blower 24 in the blower housing 23. It is configured.
Here, the scraping auger 21 is provided with a substantially cylindrical member having a spiral projection on the outer peripheral surface thereof, so that the axial direction is along the left-right direction y of the fuselage and close to the ground. It is arranged.
Both ends of the take-up auger 21 are pivotally supported by the auger housing 22 so as to be rotatable about its axis, and are driven to rotate by a driving force from the engine 31.

The auger housing 22 is a structure that pivotally supports the scraping auger 21, and has a function as a casing of the scraping auger 21.
The blower housing 23 is a housing in which the blower 24 is provided, and has a mechanism as a structure that supports the auger housing 22.

The blower 24 is configured to cause the snow transported into the blower housing 23 by the take-up auger 21 to jump toward the shooter 25 by being rotationally driven by a driving force from the engine 31. ing.
Here, the shooter 25 is a cylindrical member, and can be turned around a turning axis along a vertical direction with respect to a horizontal plane of the blower housing 23, and a tip portion thereof is along a horizontal direction. It can be rotated up and down around the rotation axis.

  By providing such a configuration, the working unit 20 travels the work vehicle 1 through the shooter 25 through the shooter 25 that has been transported into the blower housing 23 by the scraping auger 21 and has been blown off by the blower 24. In addition to being removed from the road, the position of snow falling through the shooter 25 and falling on the ground can be adjusted.

The engine 31 is provided in a drive unit 30 disposed in the machine body front-rear direction x rear x2 of the working unit 20.
The HST 102 is provided in a transmission 100 disposed below the driving unit 30.

  The drive unit 30 transmits a driving force from the engine 31 to the working unit 20 via a work driving force transmission unit 12 such as a pulley and a belt, and travel driving force transmission unit 13 such as a pulley and a belt. The driving force can be transmitted to the transmission 100 via the transmission.

Specifically, the engine 31 has an output shaft 31a protruding from a front portion, and the output shaft 31a is supported by a bracket 11 provided in the body frame 10 through a bearing (not shown) in the middle. ing.
Here, the work driving force transmission means 12 is of a belt pulley type, and is provided on a pulley 131 a for transmitting power from the output shaft 31 a of the engine 31 and an input shaft 20 a of the working unit 20. A pulley 133a and a pulley 131a and a belt 134a wound around the pulley 133a are provided.

The transmission 100 is configured to transmit the driving force from the engine 31 to the traveling units 40L and 40R so that the working vehicle 1 can move forward or backward.
The transmission 100 includes a transmission case 101 in addition to the HST 102, and an input shaft 104 projects forward from the transmission case 101. The input shaft 104 is pivotally supported by the bracket 11 at the front end.
Here, the travel driving force transmission means 13 is of a belt pulley type, and a pulley 131b provided on the output shaft 31a of the engine 31 and a pulley 133b provided on the input shaft 104 of the transmission 100. And a belt 134b wound around the pulley 131b and the pulley 133b.

The drive unit 30 further includes a generator 310 (see FIG. 4 described later) that generates electric power by the rotational power of the engine 31.
The driving unit 30 rotates the generator 310 by the engine 31 to generate electric power by the generator 310, and the battery 32 is charged with the electric power generated by the generator 310.
The drive unit 30 supplies power to the drive circuits of the left electric motor 33L and the right electric motor 33R by the charged battery 32 (and the generator 310), and the electric motor 33L is supplied by the drive circuit. The electric motors 33L and 33R can be driven while controlling the rotational speed of the motors 33R.
By providing such a configuration, the working vehicle 1 can turn right or turn left.

FIG. 3 is a skeleton diagram of the working vehicle 1 shown in FIGS. 1 and 2.
Here, the HST 102 includes a pump shaft (the input shaft) 104, a pump main body 105, a motor main body 106, a motor shaft (output shaft) 107, and an output adjustment member 108.

The pump shaft 104 is operatively connected to the engine 31, and the pump body 105 is supported by the pump shaft 104 so as not to be relatively rotatable.
The motor body 106 is fluidly connected to the pump body 105 via a pair of hydraulic oil lines 109, and the motor shaft 107 is configured to be rotated about the axis by the motor body 106. Yes.
And the said output adjustment member 108 is comprised so that the oil supply-and-discharge amount of at least one of the said pump main body 105 or the said motor main body 106 (here the said pump main body 105) can be changed.

In this example, the pump body 105 and the motor body 106 are fixed to the rear end portion of the transmission case 101.
Here, the pump main body 105 is a variable displacement piston pump, and the output adjusting member 108 includes a movable swash plate.

When the plate surface of the movable swash plate is perpendicular to the axial direction of the pump shaft 104, the HST 102 can convey pressure oil to the motor body 106 even if the pump shaft 104 is driven to rotate. When the plate surface of the movable swash plate is tilted with respect to the axial direction of the pump shaft 104, pressure oil is applied to the motor body 106 in conjunction with the rotational drive of the pump shaft 104. The motor shaft 107 can be rotated by being conveyed.
The movable swash plate is configured such that the tilt angle of the pump shaft 104 with respect to the axial direction of the pump shaft 104 is adjusted, so that the motor is driven from the pump body 105 through the pair of hydraulic oil lines 109 while the pump shaft 104 rotates once. The amount of pressure oil conveyed to the main body 106, that is, the rotational speed of the motor shaft 107 can be adjusted.

  Here, the motor main body 106 is a constant capacity motor. However, the present invention is not limited to this, and both the pump body 105 and the motor body 106 may be of a variable capacity type, the pump body 105 may be a constant capacity type, and the motor body 106 may be of a capacity. It may be variable.

The pulley 133b is fitted and fixed to the pump shaft 104, and a bevel gear 135 is fixed to the motor shaft 107.
The transmission 100 further includes first and second transmission shafts 136 and 115 and a pair of left and right differential mechanisms 103L and 103R.
A bevel gear 137 and a sprocket 139 are fitted and fixed to the first transmission shaft 136, and a sprocket 140 is fitted and fixed to the second transmission shaft 115. A braking mechanism may be interposed in a traveling system transmission path from the engine 31 to the traveling units 40L and 40R. For example, the first transmission shaft 136 may be provided with a brake 138 that can brake the rotation of the first transmission shaft 136.

The bevel gear 137 in the first transmission shaft 136 and the bevel gear 135 in the motor shaft 107 are engaged with each other, and the sprocket 139 and the second transmission shaft 115 in the first transmission shaft 136 are engaged. A chain 141 is wound around the sprocket 140 in FIG.
With this configuration, the transmission 100 transmits the driving force transmitted from the HST 102 to the first transmission shaft 136 via the bevel gear 135 and the bevel gear 137, the sprocket 139, the chain 141, and the sprocket 140. It can be transmitted to the second transmission shaft 115 via this.

  The differential mechanisms 103L and 103R are configured to be substantially symmetrical. Accordingly, since the left and right configurations are substantially the same, in the following description, the left differential mechanism 103L will be mainly described, and the right differential mechanism 103R is shown in parentheses.

A sun gear (hereinafter referred to as a sun gear) 110L (110R) in the differential mechanism 103L (103R) is externally fitted and fixed to the left half (right half) of the second transmission shaft 115, and a plurality of planetary gears (hereinafter referred to as planetary gears). And 111L (111R). The carrier 112L (112R) is a substantially disk-shaped member that is fitted and fixed to one end of the travel drive shaft 113L (113R) and rotates integrally with the travel drive shaft 113L (113R).
A plurality of rotating shafts 114L (114R) project from the surface of the carrier 112L (112R) located on the opposite side of the travel drive shaft 113L (113R), and the plurality of rotating shafts 114L (114R) respectively A plurality of planetary gears 111L (111R) are rotatably supported.

The plurality of planetary gears 111L (111R) mesh with the sun gear 110L (110R). The second transmission shaft 115 is pivotally supported on the carrier 112L (112R) via a bearing (not shown) at the left end (right end).
The ring gear 116L (116R) has a gear portion formed on the inner peripheral surface and the outer peripheral surface to form a substantially ring-shaped gear, and the gear portion on the inner peripheral surface side and the plurality of planetary gears 111L (111R) mesh with each other. It is supposed to be.

The pair of left and right electric motors 33L and 33R are fixed to the outer surface of the mission case 101. The output shafts 117L and 117R of the electric motors 33L and 33R are inserted into the mission case 101, respectively.
A warm-up gear 118L is externally fitted and fixed to the output shaft 117L of the left electric motor 33L. The warm-up gear 118L and the outer peripheral surface side of the ring gear 116L of the left differential mechanism 103L. The gear portion meshes with each other.
Similarly, a warm-up gear 118R is fitted and fixed to the output shaft 117R of the right electric motor 33R, and the outer peripheral surface side of the warm-up gear 118R and the ring gear 116R of the right differential mechanism 103R. Are engaged with each other.

Here, the traveling portions 40L and 40R are a pair of left and right, and include the pair of left and right traveling drive shafts 113L and 113R, respectively.
Specifically, in the present example, the traveling units 40L and 40R are each of a crawler type, and are disposed on both sides of the body frame 10 in the left-right direction (see FIG. 2). It is assumed that it is configured substantially symmetrically.
The traveling units 40L and 40R may be wheel type.

As shown in FIGS. 1 and 2, the pair of left and right traveling drive shafts 113L and 113R protrude outward in the lateral direction y of the body of the transmission 100. Here, the tracks in the traveling portions 40L and 40R It penetrates through the bearings (illustration omitted) in the part near the rear part of the frames 41L and 41R.
Drive sprockets 42L and 42R are fixed to the outer ends of the travel drive shafts 113L and 113R outside the track frames 41L and 41R.

Both ends of the driven shaft 45 disposed substantially parallel to the pair of left and right traveling drive shafts 113L and 113R are passed through the front frame portions of the track frames 41L and 41R via bearings (not shown). .
Drive sprockets 43L and 43R are fixed to both ends of the driven shaft 45 outside the track frames 41L and 41R. The drive sprockets 42L and 42R and the driven sprockets 43L and 43R are respectively The crawler belts 44L and 44R are wound around.

  Here, the shaft connecting the front portions of the left and right track frames 41L and 41R and the body frame 10 are connected via an electro-hydraulic cylinder 46. The brackets 14L and 14R are supported rotatably on the pair of left and right traveling drive shafts 113L and 113R via bearings (not shown), respectively.

The shift operation member 53 is provided in the driving operation unit 50.
Specifically, here, the speed change operation member 53 is a travel speed change lever that can be manually operated to change the speed of the HST 102.

In the work vehicle 1 described above, the driving force from the engine 31 is transmitted to the working unit 20 via the work driving force transmission means 12 and the transmission 100 via the travel driving force transmission means 13. Is transmitted to.
In the working unit 20, the driving auger 21 and the blower 24 are driven by the driving force from the engine 31.

  On the other hand, in the transmission 100, when the speed change operation member 53 is changed in the HST 102, the driving force transmitted to the transmission 100 is transmitted from the HST 102 to the motor shaft (output shaft) 107, the bevel gear 135, The bevel gear 137, the transmission shaft 136, the sprocket 139, the chain 141, the sprocket 140 and the transmission shaft 115 are transmitted to the sun gears 110L and 110R of the pair of left and right differential mechanisms 103L and 103R.

The driving force transmitted to the differential mechanism 103L is transmitted to the driving sprocket 42L of the traveling unit 40L via the sun gear 110L, the planetary gear 111L, the rotating shaft 114L, the carrier 112L, and the output shaft 113L.
The driving force transmitted to the differential mechanism 103R is transmitted to the driving sprocket 42R of the traveling unit 40R via the sun gear 110R, the planetary gear 111R, the rotating shaft 114R, the carrier 112R, and the output shaft 113R. The
In this way, the driving force from the engine 31 is transmitted to the pair of left and right traveling units 40L, 40R, and the traveling units 40L, 40R are rotationally driven.

The work vehicle 1 includes a work clutch device 132a inserted in a work system transmission path from the engine 31 to the work unit 20, and a work clutch operation for performing a manual operation on the work clutch device 132a. And a member 54.
The work clutch device 132a can be switched between a clutch engagement position where the clutch is engaged and a clutch disengagement position where the clutch is disengaged.
The work clutch device 132a has a power transmission state (clutch engagement state) in which power is transmitted from the engine 31 to the working unit 20 by switching between the clutch engagement position and the clutch disengagement position. The engine 31 is configured to be in a power cut-off state (clutch cut-off state) in which power from the engine 31 to the working unit 20 is cut off.

Here, the work clutch device 132 a is disposed on the pulley 131 a in the work driving force transmission means 12.
The work clutch device 132a switches between the clutch engagement position and the clutch disengagement position, thereby supporting the power transmission state (here, the pulley 131a is supported on the output shaft 31a so as not to be relatively rotatable). State, that is, a state in which power from the engine 31 can be transmitted) and the power cut-off state (here, the pulley 131a is supported on the output shaft 31a so as to be relatively rotatable about an axis, that is, the engine The state in which the power from 31 is cut off).

  The work clutch operation member 54 is configured to selectively switch between a clutch engagement position and a clutch disengagement position of the work clutch device 132a. Here, the work clutch operation member 54 is a work clutch switch that can be manually operated. It is provided in the driving operation unit 50 (see FIGS. 1 and 2).

  With such a configuration, the work vehicle 1 is driven from the engine 31 to the work unit 20 when the work clutch device 132a is in a power transmission state based on an artificial operation of the work clutch operation member 54. When the force is transmitted and the working clutch device 132a is in a power cut-off state, the driving force from the engine 31 to the working unit 20 is cut off.

Here, the driving operation unit 50 includes a steering handle 51 and an operation box 55 for performing a steering operation of the traveling units 40L and 40R.
Here, the steering handle 51 is substantially U-shaped in plan view (see FIG. 2), and a pair of support rods 51a and 51a are provided at both ends. The pair of support rods 51a, 51a extend forward and downward, respectively (see FIG. 1), and are connected to the pair of left and right brackets 14L, 14R.
The speed change operation member 53 and the work clutch operation member 54 are provided on the steering handle 51. A battery stand 57 is installed between the pair of support rods 51a and 51a.

Next, a control example of the work vehicle 1 according to the first embodiment of the present invention will be described with reference to FIGS.
FIG. 4 is a system block diagram showing a schematic configuration of a control system of the working vehicle 1 according to the first embodiment.

  As shown in FIG. 4, the working vehicle 1 according to the first embodiment includes the travel units 40L and 40R, the work unit 20, the HST 102 and the shift operation member 53, an engine output detection device 310, and a travel output detection device 320. , An operation amount detection device 330 and a control unit 200 are provided. Note that the engine output detection device 310, the travel output detection device 320, and the operation amount detection device 330 are shown only in the block diagram of FIG. 4, and are not shown in FIGS.

The output adjustment member 108 in the HST 102 is configured to be adjusted to a position corresponding to the operation amount of the speed change operation member 53.
The output adjusting member 108 can be electrically driven and can be adjusted in position based on an operation signal from the control unit 200.

Specifically, the output adjusting member 108 includes, in addition to the movable swash plate 108 ', an HST transmission motor 108a capable of changing the tilt angle of the plate surface of the movable swash plate 108' with respect to the axial direction of the pump shaft 104; And an HST output adjustment position detecting device 108b for detecting the position of the movable swash plate 108 '.
The HST transmission motor 108a changes the tilt angle of the plate surface of the output adjustment member 108 based on an operation signal from the control unit 200, whereby at least one of the pump body 105 or the motor body 106 ( Here, the HST transmission motor drive that drives the HST transmission motor 108a to the output system of the control unit 200 so that the rotation output of the HST 102 can be changed by changing the supply / discharge oil amount of the pump body 105). It is electrically connected via the part 108a ′.
Here, the HST output adjustment position detection device 108 b is an HST shift angle sensor that detects the tilt angle of the plate surface of the movable swash plate 108 ′ in the HST 102, and the detection signal is transmitted to the control unit 200. As described above, the control unit 200 is electrically connected to the input system.

The engine output detection device 310 is configured to detect the output rotational speed of the engine 31.
Here, the engine output detection device 310 is the generator that generates electric power by the rotational power of the engine 31, and the control is performed so that the power generation signal of the generator is transmitted to the control unit 200. The unit 200 is electrically connected to the input system.

The travel output detection device 320 is configured to detect the rotational output of the HST 102.
Specifically, the travel output detection device 320 is an HST output rotation state detection sensor that detects the rotation state of the motor shaft (output shaft) 107 in the HST 102. Here, the rotation of the motor shaft 107 is detected. An HST rotation speed sensor 321 for detecting the speed and an HST rotation direction sensor 322 for detecting the rotation direction of the motor shaft 107 are included.
The HST rotation speed sensor 321 is electrically connected to an input system of the control unit 200 so that a detection signal related to the rotation speed of the motor shaft 107 is transmitted to the control unit 200.
The HST rotation direction sensor 322 is electrically connected to an input system of the control unit 200 so that a detection signal related to the rotation direction of the motor shaft 107 is transmitted to the control unit 200.

The operation amount detection device 330 is configured to detect an operation amount of the speed change operation member 53.
Here, the operation amount detection device 330 is a shift lever angle sensor that detects an operation angle of the shift operation member 53, and a detection signal related to the operation angle of the shift operation member 53 is transmitted to the control unit 200. In this way, the control unit 200 is electrically connected to the input system.

The control unit 200 receives detection signals from the engine output detection device 310, the travel output detection device 320, and the operation amount detection device 330, and outputs a control signal for the output adjustment member 108 in the HST 102. It is comprised and is provided with the control apparatus 210 and the memory | storage part 220. FIG.
Specifically, the control device 210 includes a central processing unit (CPU) and includes control calculation means for executing various calculation processes.
The storage unit 220 stores a control program including a control example of the work vehicle 1 according to the first embodiment and necessary functions, and includes a ROM 221 and a RAM 222, for example.

The ROM 221 is configured to store the control program and to store predetermined data relating to an arithmetic expression or a lookup table described later. The CPU 210 is configured to load the control program stored in the ROM 221 into the RAM 222 as necessary and execute the control program. The RAM 222 is used when the control program is executed by the CPU 210, and is configured to temporarily hold data generated during the execution.
The storage unit 220 stores a deceleration rate conversion calculation formula and a reference output conversion calculation formula, which will be described later, in advance.

The control unit 200 for carrying out a control example of the work vehicle 1 of the first embodiment decelerates based on a detection result of the engine output detection device 310 with respect to a reference output corresponding to the operation amount of the speed change operation member 53 A load control mode is provided for controlling the operation of the output adjusting member 108 using the output multiplied by the rate as the target rotation output of the HST 102.
That is, in the load control mode, the target rotation output of the HST 102 is obtained by multiplying the reference output corresponding to the operation amount of the shift operation member 53 by the deceleration rate based on the detection result of the engine output detection device 310. Thus, the operation of the output adjusting member 108 is controlled.
In the load control mode, based on a signal from the engine output detection device 310, when the output rotation speed of the engine 31 exceeds the first threshold, the deceleration rate is set to 1, and the output rotation of the engine 31 is When the number becomes equal to or less than the first threshold value, a deceleration rate corresponding to the output rotation speed is selected.
Here, the load control mode is configured to select a deceleration rate that decreases as the output rotational speed decreases when the output rotational speed of the engine 31 becomes equal to or less than the first threshold value.

FIGS. 5 to 7 are graphs for explaining a control example of the working vehicle 1 of the first embodiment. FIG. 5 is a graph showing the deceleration rate Y with respect to the rotational speed X of the engine 31. FIG. 6 is a graph showing the reference vehicle speed Va of the work vehicle 1 (that is, the reference output of the HST 102) with respect to the operation amount θ of the speed change operation member 53. FIG. 7 is a graph showing the target vehicle speed Vb of the working vehicle 1 (that is, the target rotational output of the HST 102) with respect to the rotational speed X of the engine 31.
5 and 7, “Xf” indicates the first threshold value. In FIG. 6, the horizontal axis indicates the operation angle θ from the neutral position (0 °) of the speed change operation member 53, the plus side indicates the forward direction angle, and the minus side indicates the reverse direction angle. Yes.
6 and 7, the work speed indicates the operation angle and the vehicle speed of the speed change operation member 53, which is a guideline for work, and the travel speed indicates the speed change operation member, which is a guideline for movement. 53 shows the operation angle and vehicle speed.

The control unit 200 includes a neutral control mode in which the operation of the output adjustment member 108 is controlled so that the position of the output adjustment member 108 is positioned at the neutral position (that is, the work vehicle 1 stops). .
That is, the control unit 200 determines that the position of the output adjustment member 108 detected by the HST output adjustment position detector 108b (here, the tilt angle of the plate surface of the movable swash plate 108 ') corresponds to the neutral position. The output adjusting member 108 can be controlled to operate (HST shift angle control) so as to be located at a position (here, a tilt angle).

In the working vehicle 1 according to the first embodiment, as shown in FIG. 5, when the output rotational speed X of the engine 31 exceeds the first threshold value Xf (that is, the load on the engine 31 is greater than a predetermined load). In the case of small), the output obtained by multiplying the reference output (see FIG. 6) according to the operation amount of the speed change operation member 53 by 1 (100%: see G in FIG. 5) as the deceleration rate Y, The output adjusting member 108 can be controlled to operate as a target rotation output of the HST 102 (target vehicle speed Vb of the working vehicle 1; see g in FIG. 7). As a result, even if a load is applied to the traveling units 40L and 40R, if the load on the engine 31 is smaller than a predetermined value, the output of the HST 102 can be maintained at the reference output, so that a reduction in vehicle speed can be prevented. As a result, a reduction in work efficiency can be prevented as much as possible.
On the other hand, as shown in FIG. 5, when the output rotational speed of the engine 31 becomes equal to or less than the first threshold value Xf (that is, when the load on the engine 31 becomes equal to or higher than the predetermined load), the operation of the speed change operation member 53 is performed. Deceleration rate Y corresponding to the output rotational speed with respect to the reference output corresponding to the amount (see FIG. 6) (here, the deceleration rate Y that decreases as the output rotational speed decreases: refer to AF in FIG. 5) ) Is used as the target rotation output of the HST 102 (the target vehicle speed Vb of the working vehicle 1; see a to f in FIG. 7), and the output adjusting member 108 can be controlled. Thereby, the overload to the engine 31 can be prevented.
As described above, according to the work vehicle 1 according to the first embodiment, it is possible to prevent a reduction in work efficiency as much as possible while preventing an overload to the engine 31.
Further, since overload to the engine 31 can be prevented, engine stall can be prevented as much as possible.
Further, when the output rotational speed of the engine 31 is equal to or lower than the first threshold value, the vehicle speed can be automatically controlled in accordance with the output rotational speed, so that the troublesome adjustment of the traveling speed can be eliminated, thereby improving the efficiency of work. It can be performed.
Furthermore, in this example, the snow removal capability can be kept optimal while ensuring a constant snow throw distance.

In addition to the above-described configuration, the control unit 200 includes a second threshold value Xa in which the output rotation speed of the engine 31 is smaller than the first threshold value Xf based on a signal from the engine output detection device 310 in the load control mode. In the following, the operation of the output adjusting member 108 is controlled so that the rotation output of the HST 102 becomes zero.
By providing such a configuration, the work vehicle 1 can reliably prevent engine stall even when a load is applied to the engine 31 such that the output rotation speed of the engine 31 is less than or equal to the second threshold value Xa. It becomes possible to do.

The work vehicle 1 according to the first embodiment will be described more specifically. The control unit 200 detects the operation amount of the shift operation member 53 by the operation amount detection device 330, and the operation amount detection device 330 Based on the detected value, a reference output corresponding to the operation amount of the speed change operation member 53 is obtained.
Further, the control unit 200 is configured to detect the output rotation speed X of the engine 31 by the engine output detection device 310 and obtain the deceleration rate Y based on the detection result of the engine output detection device 310. .

The control unit 200 is configured to multiply the reference output by a deceleration rate Y based on the detection result of the engine output detection device 310.
The control unit 200 is configured to control the operation of the output adjustment member 108 using an output obtained by multiplying the reference output by a deceleration rate Y as a target rotation output of the HST 102.

  In addition to the above configuration, the control unit 200 has detection values of the HST output adjustment position detection device 108b and the operation amount detection device 330 within a normal range (for example, an output voltage of 0.1 V to 4.9 V). It may be configured to determine whether or not there is, and when the detected value is not within the normal range, fail processing such as error display may be executed.

The work vehicle 1 according to the first embodiment includes the work clutch device 132a and the work clutch operation member 54 in addition to the above configuration.
As shown in FIG. 4, the work clutch device 132 a is configured to be electrically driven, and based on an operation signal from the control unit 200, the power transmission state (clutch engagement state) and the power cut-off state (clutch) It is electrically connected to the output system of the control unit 200 so as to be able to take a cut-off state.
The work clutch operating member 54 is electrically connected to an input system of the control unit 200 so that a detection signal related to the clutch engagement position of the work clutch device 132a or a detection signal related to the clutch disengagement position is transmitted to the control unit 200. It is connected to the.

The working vehicle 1 according to the first embodiment includes a travel switch 52a in addition to the above configuration. The travel switch 52a is operated by a travel operation member 52 that can be manually operated.
As illustrated in FIG. 4, the travel switch 52 a is configured to transmit a switching signal for switching between a vehicle travel state in which the vehicle travels and a vehicle stop state in which the vehicle is stopped to the control unit 200. It is electrically connected to the input system.
Here, the travel operation member 52 is energized so that the travel switch 52a can be switched to a vehicle stop state, and is a travel lever in the form of a deadman clutch lever. The travel operation member 52 is provided in the driving operation unit 50 (see FIGS. 1 and 2).

The working vehicle 1 is in a vehicle stop state (here, the travel switch 52a) when the travel operation member 52 is released from the vehicle travel state (here, the position where the travel switch 52a is switched to the vehicle travel state). The working clutch device 132a is configured to shift to a power cut-off state.
In addition, when the work clutch operation member 54 is manually operated to the clutch engagement position after the travel operation member 52 is manually operated in the vehicle travel state, the work vehicle 1 is operated by the work clutch operation member 54. Is configured to maintain the clutch engagement position until the travel operation member 52 is manually operated in a vehicle stop state.
In addition, even when the travel operation member 52 is manually operated while the vehicle is stopped, the work vehicle 1 is in a state where the work clutch operation member 54 is continuously operated to the clutch engagement position. It is comprised so that the state of an alignment position may be hold | maintained.

Next, a control example of the first embodiment will be described in detail below with reference to FIG.
FIG. 8 is a flowchart showing a flow of a control example of the work vehicle 1 according to the first embodiment.

In the control example of the work vehicle 1 according to the first embodiment, as shown in FIG. 8, it is first determined whether or not the work clutch operating member 54 is operated to the clutch engagement position (step S1).
If it is determined in step S1 that the work clutch operating member 54 has been operated to the clutch engagement position, the process proceeds to step S2, and if it is determined that the clutch is disengaged, the process proceeds to step S4. .

Next, when it is determined in step S1 that the work clutch operation member 54 is operated to the clutch engagement position, the operation amount detection device 330 detects the operation amount of the speed change operation member 53 (step S2). ), The process proceeds to step S3.
Next, it is determined whether or not the operation position is on the forward side according to the operation amount of the speed change operation member 53 (here, whether or not the operation angle θ of the speed change operation member 53 is on the plus side) ( Step S3).
If it is determined in step S3 that the operation position of the speed change operation member 53 is located on the forward side, the process proceeds to step S6, and if it is determined that the operation position is on the neutral position or the reverse side, The process proceeds to step S4.

  If it is determined in step S3 that the operation position is in the neutral position or the reverse side, or if it is determined in step S1 that the work clutch operation member 54 is operated in the clutch disengagement position, The deceleration rate Y is set to 1 (100%) (step S4), and the process proceeds to step S5.

On the other hand, if it is determined in step S3 that the operation position is located on the forward side, the engine output detection device 310 detects the output rotational speed X of the engine 31 (step S6), and the detection is performed. Deceleration rate Y is determined from output rotational speed X (step S7), and the process proceeds to step S5.
Specifically, in step S7, the output rotational speed X of the engine 31 detected in step S6 is calculated from the output rotational speed X using the deceleration rate conversion calculation formula stored in the storage unit 220. Is converted into a deceleration rate Y corresponding to.

Here, as shown in FIG. 5, the calculation formula for conversion of the deceleration rate is such that the output rotational speed X of the engine 31 and the corresponding deceleration rate Y are associated with each other.
More specifically, the deceleration rate conversion calculation formula is composed of a plurality of primary formulas (here, the following formulas (A) to (G)) having different slopes.

Expression (A) is an expression when the output speed X of the engine 31 is X ≦ Xa (when the output speed X is equal to or less than the second threshold value Xa), and the deceleration rate Y = Ya ′. Yes.
Expression (B) is an expression when the output rotational speed X of the engine 31 is Xa <X ≦ Xb, and the deceleration rate Y = (Ya−Yb) / (Xa−Xb) × (X−Xa) + Ya Has been.
Expression (C) is an expression when the output rotational speed X of the engine 31 is Xb <X ≦ Xc, and the deceleration rate Y = (Yb−Yc) / (Xb−Xc) × (X−Xb) + Yb Has been.
Expression (D) is an expression when the output rotational speed X of the engine 31 is Xc <X ≦ Xd, and the deceleration rate Y = (Yc−Yd) / (Xc−Xd) × (X−Xc) + Yc Has been.
Expression (E) is an expression when the output rotational speed X of the engine 31 is Xd <X ≦ Xe, and the deceleration rate Y = (Yd−Ye) / (Xd−Xe) × (X−Xd) + Yd Has been.
Expression (F) is an expression when the output rotational speed X of the engine 31 is Xe <X ≦ Xf, and the deceleration rate Y = (Ye−Yf) / (Xe−Xf) × (X−Xe) + Ye Has been.
The expression (G) is an expression when the output rotation speed X of the engine 31 is Xf <X (when the output rotation speed X exceeds the first threshold value Xf), and the deceleration rate Y = Yf. Yes.
In the example of FIG. 5, Xa (second threshold value) is 1500 (times / minute), Ya ′ is 0 (0%), and Ya is 0 <Ya <0.06 (6%). Xb is 2000 (times / minute), and Yb is 0.06 (6%). Xc is 2500 (times / minute), and Yc is 0.12 (12%). Xd is 3000 (times / minute), and Yd is 0.24 (24%). Xe is 3500 (times / minute), and Ye is 0.6 (60%). Xf (first threshold value) is 3800 (times / minute), and Yf is 1 (100%).

  Here, the deceleration rate Y is converted using the deceleration rate conversion formula, but an LUT (lookup table) corresponding to the deceleration rate conversion formula is stored in the storage unit 220 in advance. It may be converted using the LUT.

Next, the deceleration rate Y set in step S4 or step 7 is stored in the storage unit 220 (step S5), and it is determined whether or not the travel switch 52a is switched to the vehicle travel state (step S8). ).
If it is determined in step S8 that the travel switch 52a has been switched to the vehicle travel state, the process proceeds to step S9. If it is determined that the travel switch 52a has been switched to the vehicle stop state, the process proceeds to step S14. .

  If it is determined in step S8 that the travel switch 52a has been switched to the vehicle travel state, whether the detection values of the HST output adjustment position detection device 108b and the operation amount detection device 330 are within a normal range. (Step S9), if both the detected values are within the normal range, the process proceeds to step S10, and if both the detected values are not within the normal range, the process proceeds to step S13. To do.

If it is determined in step S9 that the detected value is within the normal range, a reference output of the HST 102 corresponding to the operation amount of the speed change operation member 53 is obtained (step S10), and the process proceeds to step S11.
Specifically, in step S10, using the reference output conversion arithmetic expression stored in the storage unit 220, the operation amount θ of the speed change operation member 53 is set to the value of the HST 102 corresponding to the operation amount θ. Convert to standard output.

Here, as shown in FIG. 6, the reference output conversion arithmetic expression is obtained by associating the operation amount θ of the speed change operation member 53 with the corresponding reference vehicle speed Va (reference output of the HST 102). Has been.
Here, the reference output of the HST 102 is converted using the reference output conversion arithmetic expression, but an LUT (lookup table) corresponding to the reference output conversion arithmetic expression is stored in the storage unit 220 in advance. It may be stored and converted using the LUT.

Next, as shown in the following equation (1), the reference output of the HST 102 is multiplied by the deceleration rate Y stored in the storage unit 220 (step S11). Then, the relationship between the target vehicle speed Vb of the working vehicle 1 (the target rotation output of the HST 102) and the rotational speed X of the engine 31 is as shown in FIG.
HST102 target rotation output = HST102 reference output × deceleration rate Y (1)
In such a formula, when the output rotational speed X of the engine 31 exceeds the first threshold value Xf (when the load on the engine 31 is lighter than a predetermined load), the target rotational output of the HST 102 is When the output rotational speed X of the engine 31 is equal to or less than the first threshold value Xf (when the load on the engine 31 is equal to or higher than a predetermined load), the target rotational output of the HST 102 is the reference output. Reduced with respect to output.
In step S12, the output adjustment member 108 is controlled to operate with the output obtained by multiplying the reference output by the deceleration rate Y as the target rotation output of the HST 102, and the process proceeds to step S16.
As shown in FIG. 9, the deceleration rate Y is a constant deceleration rate (Yf ′ to Yc ′) until the output rotational speed of the engine 31 reaches one threshold value (Xe ′ to Xb ′). , It may be configured to be a constant value (Ye ′ to Yb ′) smaller than the one deceleration rate when the value is equal to or less than the one threshold value (Xe ′ to Xb ′). By doing so, the speed reduction rate does not decrease until the output speed of the engine 31 reaches one threshold (Xe ′ to Xa ′), and the speed reduction rate is constant (Yf ′ to Yb ′). Therefore, the working efficiency can be improved accordingly.

On the other hand, if it is determined in step S9 that the detected value is not within the normal range, a failure process such as error display is executed (step S13), and the process proceeds to step S15.
If it is determined in step S8 that the travel switch 52a has been switched to the vehicle stop state, in step S14, the output adjustment member 108 is positioned so that the output adjustment member 108 is positioned at the neutral position. Is controlled (neutral control (HST shift angle control)), and the process proceeds to step S15.

  In step S15, it is determined whether or not the operation has ended. If it is determined that the operation has not ended, the process proceeds to step S1, and the processing in steps S1 to S14 is repeated while the operation has ended. If it is determined, the process is terminated.

In addition to the above-described configuration, the control unit 200 includes the deceleration rate when the output speed of the engine 31 is equal to or less than the first threshold value Xf and greater than the second threshold value Xa in the load control mode. When the target rotation output after multiplication by Y falls below a predetermined minimum output, the operation of the output adjusting member 108 may be controlled so that the rotation output of the HST 102 becomes the minimum output. Good.
By providing such a configuration, the work vehicle 1 can maintain the target rotation output at the minimum output even when the target rotation output after multiplication of the deceleration rate falls below a predetermined minimum output, and the work efficiency is increased accordingly. Can be improved.

In this case, as shown in FIG. 10, the processing of step S111 and step S112 can be provided between the processing of step S11 and the processing of step S12 in the flowchart of FIG.
In the process shown in FIG. 10, it is determined whether or not the target rotation output multiplied by the deceleration rate Y in step S11 is below a predetermined minimum output (see the chain line α in FIG. 7) (step S111). When the output is equal to or higher than the minimum output α, the process proceeds to step S13. On the other hand, when the output is below the minimum output α, the output adjusting member 108 is set so that the rotational output of the HST 102 becomes the minimum output α. The operation is controlled (step S112), and the process proceeds to step S15.

Next, an example of control of the work vehicle 1 according to the second embodiment will be described with reference to FIGS. 11 and 12.
FIG. 11 is a system block diagram illustrating a schematic configuration of a control system of the work vehicle 1 according to the second embodiment.

  The work vehicle 1 according to the second embodiment further includes a changeover switch 56 that can be manually operated, and has substantially the same configuration as the work vehicle 1 of the first embodiment, except that the control unit 200 has a different control program. is doing. Accordingly, members having the same configuration and action are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown in FIG. 11, the changeover switch 56 is electrically connected to the input system of the control unit 200 so that a changeover signal for switching between a vehicle speed control mode and a load control mode, which will be described later, is transmitted to the control unit 200. It is connected to the.
The storage unit 220 in the control unit 200 stores a control program including a control example of the work vehicle 1 according to the second embodiment and necessary functions.

The control unit 100 for carrying out a control example of the work vehicle 1 of the second embodiment controls the operation of the output adjusting member 108 with a reference output corresponding to the operation amount of the speed change operation member 53 as a target rotation output of the HST 102. A vehicle speed control mode is provided.
That is, the vehicle speed control mode is configured to control the operation of the output adjustment member 108 so that the target rotation output of the HST 102 becomes a reference output corresponding to the operation amount of the speed change operation member 53.
With such a configuration, the work vehicle 1 always outputs a reference output corresponding to the operation amount of the speed change operation member 53 without being affected by disturbances such as traveling on an uphill or rotation of the engine. Can be maintained. Accordingly, the vehicle speed can be made constant on any road surface or slope according to the operation amount of the speed change operation member 53.
The control unit 100 is configured so that the vehicle speed control mode or the load control mode is switched by the changeover switch 56.

  According to the working vehicle 1 according to the second embodiment, for example, it is possible to switch to the load control mode by the changeover switch 56 during work, and to switch to the vehicle speed control mode by the changeover switch 56 during non-working.

Next, a control example of the work vehicle 1 according to the second embodiment will be described in detail below with reference to the flowchart of FIG. FIG. 12 is a flowchart showing a flow of a control example of the work vehicle 1 according to the second embodiment.
Note that the vehicle speed control mode can be a process after step S4 with a deceleration rate of 1 in the flowchart shown in FIG. Therefore, in the flowchart shown in FIG. 12, step S0 is provided before step S1 in the flowchart shown in FIG.
In the following, description of portions common to the flowchart shown in FIG.

In the control example of the working vehicle 1 of the first embodiment, as shown in FIG. 12, first, it is determined whether or not the load control mode is switched by the changeover switch 56 (step S0), and the load control is performed. When it is determined that the mode has been switched, the process proceeds to step S1, while when it is determined that the mode has been switched to the vehicle speed control mode, the process proceeds to step S4.
In step S15, it is determined whether or not the operation has ended. If it is determined that the operation has not ended, the process proceeds to step S0, and the processing in steps S0 to S14 is repeated while the operation ends. If it is determined that the process has been completed, the process ends.

  In the first and second embodiments, the working vehicle 1 is brought into the vehicle stop state by the neutral control mode by manually operating the travel switch 52a. However, the working vehicle 1 A traveling clutch device inserted in the traveling system transmission path from the engine 31 to the traveling portions 40L, 40R, and a traveling clutch operation member for performing a predetermined artificial operation on the traveling clutch device. The working vehicle 1 may be brought into a vehicle stop state by providing and operating the traveling clutch device based on a manual operation of the traveling clutch operating member.

FIG. 1 is a schematic side view of a walking snowplow that is an example of a working vehicle according to the present invention. FIG. 2 is a schematic plan view of the walking snowplow shown in FIG. FIG. 3 is a skeleton diagram of the working vehicle shown in FIGS. 1 and 2. FIG. 4 is a system block diagram showing a schematic configuration of a control system of the work vehicle according to the first embodiment. FIG. 5 is a graph showing the deceleration rate Y with respect to the engine speed X. FIG. 6 is a graph showing the vehicle speed Va of the work vehicle with respect to the operation amount θ of the speed change operation member. FIG. 7 is a graph showing the target vehicle speed Vb of the working vehicle with respect to the engine speed X. FIG. 8 is a flowchart showing a flow of a control example of the work vehicle according to the first embodiment. FIG. 9 is a graph showing another example of the deceleration rate Y with respect to the engine speed X shown in FIG. FIG. 10 is a flowchart showing the processes of steps S121 to S122 provided between the process of step S11 and the process of step S12 in the flowchart of FIG. FIG. 11 is a system block diagram showing a schematic configuration of a control system for a working vehicle according to the second embodiment. FIG. 12 is a flowchart showing a flow of a control example of the work vehicle according to the second embodiment.

1 Working vehicle 20 Working part 31 Engine 40L, 40R Traveling part 53 Shifting operation member 56 Changeover switch 108 Output adjusting member 102 HST
200 Control Unit 310 Engine Output Detection Device 320 Traveling Output Detection Device 330 Operation Amount Detection Device Xa Second Threshold Xf First Threshold Y Deceleration Rate

Claims (2)

A traveling unit and a working unit that are driven by using an output from the engine, an HST inserted in a traveling system transmission path from the engine to the traveling unit, and a speed change operation member for speed-changing the HST An engine output detection device for detecting the output rotational speed of the engine, a travel output detection device for detecting the rotational output of the HST, an operation amount detection device for detecting an operation amount of the speed change operation member, and the engine output detection A control unit that inputs a detection signal from the device, the travel output detection device, and the operation amount detection device, and outputs a control signal of the output adjustment member in the HST,
The control unit outputs, as a target rotation output of the HST, an output obtained by multiplying a reference output corresponding to an operation amount of the speed change operation member by a deceleration rate based on a detection result of the engine output detection device. It has a load control mode that controls the operation.
In the load control mode, based on a signal from the engine output detection device, the deceleration rate is set to 1 when the output speed of the engine exceeds a first threshold, and the output speed of the engine is set to the first speed. When the engine speed falls below a threshold value, a deceleration rate corresponding to the output speed is selected, and when the engine output speed falls below a second threshold value that is smaller than the first threshold value, the output so that the HST rotation output becomes zero. When the output of the engine is controlled to be less than the first threshold and greater than the second threshold, the target rotational output after multiplication of the deceleration rate falls below a predetermined minimum output. In the working vehicle, the operation of the output adjusting member is controlled so that the rotation output of the HST becomes the minimum output . The control unit includes a vehicle speed control mode in which operation control of the output adjusting member is performed with a reference output corresponding to an operation amount of the speed change operation member as a target rotation output of the HST.
2. The work vehicle according to claim 1, wherein the vehicle speed control mode or the load control mode is switched by a manually operable changeover switch.

Images